Properties of lightly doped t-J two-leg ladders

TL;DR

This paper numerically investigates the doped t-J ladder, revealing its transition to a Luther-Emery liquid, hole pairing with d-wave symmetry, and detailed excitation spectra, providing insights into its quantum phases and excitations.

Contribution

It provides a comprehensive numerical analysis of the doped t-J ladder, elucidating its phase behavior, excitation spectrum, and comparison with 2D systems, including the Luther-Emery regime and hole pairing mechanisms.

Findings

Ladder scales to Luther-Emery liquid in strong coupling

Hole pairing with modified d-wave symmetry observed

Excitation spectrum includes quasiparticles and magnon modes

Abstract

We have numerically investigated the doped t-J ladder using exact diagonalization. We have studied both the limit of strong inter-chain coupling and isotropic coupling. The ladder scales to the Luther-Emery liquid regime in the strong inter-chain coupling limit. In this strong coupling limit there is a simple picture of the excitation spectrum that can be continued to explain the behavior at isotropic coupling. At J=0 we have indications of a ferromagnetic ground state. At a large $J/t$ the ladder is phase separated into holes and a Heisenberg ladder. At intermediate coupling the ground state shows hole pairing with a modified d-wave symmetry. The excitation spectrum separates into a limited number of quasiparticles which carry charge $+|e|$ and spin ${1\over 2}$ and a triplet magnon mode. At half-filling the former vanish but the latter evolves continuously into the magnon band of the spin liquid. At low doping the quasiparticles form a dilute Fermi gas with a strong attraction but simultaneously the Fermi wave vector, as would be measured in photoemission, is large. The dynamical structure factors are calculated and are found to be very similar to calculations on 2D clusters.